Engines will play a key role in tractor-buying decisions in 2011. That’s because on January 1, all off-road diesel engines rated 174 hp and higher must comply with the Environmental Protection Agency’s Tier 4i (interim) emissions regulations. These rules will affect high-horsepower tractors, combines, sprayers and other self-propelled vehicles used in farming.

The EPA has been regulating diesel emissions on farms since 1996. This latest round of cuts calls for a 90% reduction of particulate matter (PM), also known as soot, and a 50% drop in oxides of nitrogen, or NOx, the stuff that forms smog, in relation to Tier 3. How clean is that, you ask?

“With the new Tier 4A engines, the air coming out of the engine is so clean you can hardly see any exhaust,” says Tom Dean, marketing manager for Case IH high-horsepower tractors.

The end result is cleaner air and a healthier environment. But clean air comes at a price, which can vary according to the technology being used, making it pay to do your homework.

EGR vs. SCR

Manufacturers have employed one of two engine technologies to achieve Tier 4i requirements, both of which involve, for the first time, engine after treatments. Some manufacturers, including John Deere and Cummins (which makes engines for Versatile), are using cooled Exhaust Gas Recirculation (EGR) to reduce NOx inside the combustion chamber and a diesel particulate filter (DPF). The DPF replaces the muffler to capture particulates, which then have to be burned off through a regeneration process. Some experts question whether this process will affect vehicle operation.

Other manufacturers, including AGCO, Case IH, and New Holland, are employing Selective Catalytic Reduction (SCR) to achieve the required levels for high-horsepower equipment. This method treats exhaust gases post combustion, or after they leave the engine, with a fluid blend of urea and water, called diesel exhaust fluid (DEF).

These are the same two methods being used this year in diesel-powered cars and trucks to achieve similar emission reductions on the highway. Both methods work. But which one is better for buyers depends on whom you ask, according to Jim Mele, editor-in-chief of Fleet Owner.

“There are so many claims flying back and forth,” Mele says. “It is like a scorched earth policy between the manufacturers right now.”

Mele says that some tractor manufacturers claim that SCR offers better engine efficiency and fuel economy because it treats emissions separate from engine function. The drawback, he says, is that you have to carry DEF, which costs about the same per gallon as diesel fuel.

“The other method, EGR, doesn’t require you to add a second fluid,” Mele says. “But those against it will say it burns more fuel and shortens service intervals. It’s a he-said, she-said kind of thing.”

Off-road vs. on-road

Mele says in the trucking industry, all but one engine manufacturer — Navistar — has chosen to use SCR technology to meet its 2010 standards. But agriculture is a different application, with different duty cycles. What’s right for on-road may not be right for off-road, offers Alan Hansen, an engineer at the University of Illinois.

Hansen says a key difference between on-road and off-road engine usage is the higher levels of average torque and speed to which off-road engines are subjected. “The so-called duty cycle for an off-road engine is higher than that for on-road because there is a higher average power demand for off-road applications such as agriculture or earthmoving,” Hansen explains. “This creates differences in combustion, exhaust gas temperature and, hence, in emissions. Maybe higher exhaust gas temperatures from generating more power may facilitate the regeneration of diesel particulate filters making the EGR system viable, whereas for on-road it may not be so.”

Hansen’s colleague, Xinlei Wang, who has worked extensively with after-treatment systems, says it may be too early to tell which system is better because engine makers will face even stricter standards in 2014, when Tier 4 Final regulations go into effect.

Wang says, “Technologies to be deployed for meeting 2014 emissions regulations are still somewhat in the experimental stage and may be regarded as not being mature enough to allow definite statements to be made about the relative merits of EGR versus SCR.”

New rules?

Another perspective comes from the Nebraska Tractor Test Lab, known as the supreme court of tractor claims. The lab, located on the campus of University of Nebraska–Lincoln, conducts performance tests to verify manufacturer claims of tractors sold in the U.S.

Roger Hoy, director of the lab, says tests of new Tier 4i-compliant tractors have not been done yet because the tractors are just being launched and testing protocols are still being developed. However, the lab did test a Tier 3 tractor equipped with SCR last year.

“You can find an SCR system on the Massey Ferguson 8600 series and Challenger MT600C series tractors,” Hoy says. “AGCO installed it in some variation for Tier 3, which greatly improved their fuel economy and gave them experience with the system.”

However, the Nebraska Test Report on the Massey Ferguson 8680 states that the “DEF rate was measured at a maximum of 3% of the diesel fuel consumption,” which is an added cost buyers must consider.

“Generally as the engine worked harder creating higher combustion temperatures, more NOx was created resulting in more DEF usage,” Hoy says. “If one assumes DEF to be the same cost as diesel, you can start to compare operating costs of this tractor with a comparable model such as the John Deere 8320R.”

Hoy says a board action is under way that would require the lab to document DEF flow rates much the same as fuel flow rates when the tractors come in for official testing.

“For us and farmers, this subject will get a lot easier for everyone when we start to have some official test data to point to,” Hoy says.

For now, he advises buyers to ask plenty of questions (see “Insider’s tip sheet”). “Both the DPF and SCR systems that we have tested or observed are in my opinion well-designed systems which are not likely to have significant effects on operating costs,” Hoy says. “However, we will probably see variations of these systems that are not so well designed that may have undesirable characteristics such as exceptionally high DEF usage or active regenerations that may require the tractor to stop what it is doing in order to regenerate.”

The final round

Engine experts say choosing between the two technologies might be a moot point by 2014, when engine manufacturers must face a final round of emissions reductions. Tier 4 Final calls for near-zero levels of NOx and PM.

“The major change for Tier 4 Final is a further reduction in NOx, which may require all manufacturers of engines below 750 hp to use both SCR and cooled EGR with DPFs,” says David Combs, senior sales manager with MTU Detroit Diesel, which sells Mercedes engines for off-highway use.

Tractor makers agree that both technologies will likely be required to meet final regulations. However, all of them report that they are fervently pursuing other technologies that may reduce the burden of having to use both solutions.

“We’ve got three more years before we have to make a final decision on precisely what technology we will use,” says Case IH’s Tom Dean. “And there are new technologies coming out all the time that can help us achieve what we need to, but we’re confident the final solution will include key elements of the SCR approach we’ve introduced now for 2011.”